Fig. 4. Vasodilator responses to increase in levels of carbon dioxide (Pco2= 50 mmHg) in the absence or presence of the Ca2+-dependent K+channel antagonist iberiotoxin (10−7m) in rat cerebral parenchymal arterioles. Baseline diameters were 6.5 ± 2.3 and 6.4 ± 2.7 μm for control arterioles and arterioles treated with iberiotoxin, respectively. Vasoconstrictor responses to prostaglandin F2α(5 × 10−7m) were 18.4 ± 6.2 and 21.3 ± 5.3% for control arterioles and arterioles treated with iberiotoxin, respectively. Data are expressed as mean ± SD.